JP6201386B2 - Current estimation device - Google Patents

Description

  The present invention relates to a technique for estimating current. It is particularly suitable for a technique for estimating an alternating current input to a diode bridge that inputs a three-phase alternating voltage and outputs a direct current.

  In order to detect the harmonic current generated by the inverter circuit connected to the three-phase power supply, a technique has been proposed in which a plurality of current detection means are provided between the three-phase power supply and the rectifier circuit of the inverter circuit (below) Patent Documents 1 to 3) listed above.

  When a plurality of current detection means are used, a problem of erroneous connection to the power supply line of the three-phase power supply occurs.

JP 2008-234298 A JP 2001-091600 A JP 2011-185852 A

  In order to solve the above problem, as illustrated in Patent Documents 2 and 3, for example, a means for detecting a connection abnormality of the current detector is required.

  An object of the present invention is to provide a technique for avoiding erroneous connection of current detectors or further reducing the number of current detectors.

A current estimation apparatus according to the present invention includes a diode bridge (21) that receives a three-phase AC voltage, outputs a DC current (idc) by full-wave rectification, a reactor (25) through which the DC current flows, the power converter and a smoothing capacitor (22) connected in parallel with the series connection between the diode bridge and a reactor, the DC current the diode bridge output (idc, idc ^) to the diode bridge from It is a current estimation device that estimates an input alternating current (ir, is, it).

  And the 1st aspect has the phase calculating part (72) which detects the voltage phase of the said alternating voltage (Vr) of a 1st phase, and the estimated value (ir ^) of the said alternating current (ir) of the said 1st phase. A phase current calculation unit (76) for obtaining

  The phase current calculation unit sets the voltage phase when the polarity of the AC voltage of the first phase changes from negative to positive as 0 degrees, and the voltage phase is (i) 30 to 150 degrees with the direct current (Ii) the current of which the absolute value is the same and the polarity is different from that of the direct current at 210 to 330 degrees, and (iii) the current takes the value 0 in the other phases, the alternating current (ir) of the first phase Is an estimated value (ir ^).

DC current detector (26) is further provided for detecting the DC current (idc) from the output side of the front Symbol diode bridge in the first embodiment.

In the second aspect of the current estimation apparatus according to the present invention, from the alternating current of two phases (IAC1, IAC2), obtains the alternating current of the other one phase (IAC3), the alternating current of three phases Are further provided with a DC current calculation unit (82) for estimating the DC current (idc).

  The phase current calculation unit (76) obtains an estimated value (ir ^) of the alternating current (ir) of the first phase from the direct current (idc ^) estimated by the direct current calculation unit.

  In the second aspect, for example, an AC current detector (81a) for detecting the AC currents (iac1, iac2) of the two phases is further provided.

In the third aspect of the current estimation apparatus according to the present invention, by the 120 degrees or 240 degrees phase-shifted alternating current (IAC1) of one phase other two of said alternating current phases (IAC2, IAC3) A phase shifter (83) to be estimated, the alternating current of the one phase, and the same polarity waveform of the estimated alternating currents (iac2 ^, iac3 ^) of the other two phases are combined, A direct current calculation unit (82) for estimating the direct current (idc) is further provided.

  And the said phase current calculating part (76) obtains the estimated value (ir ^) of the said alternating current (ir) of said 1st phase from the said direct current (idc ^) estimated by the said direct current calculating part.

  In the third aspect, for example, an AC current detector (81b) that detects the AC current (iac1) of the one phase is further provided.

In the fourth aspect of the current estimation apparatus according to the present invention, the estimated value (ir ^) phase 120 degrees or 240 degrees shift of the phase current computing unit (76) the alternating current of the first phase (ir) Thus, an estimated value (is ^; it ^) of the alternating current (is; it) in the second phase is obtained. The first to third aspects of the current estimation device according to the present invention may have such a feature.

  According to the present invention, erroneous connection of current detectors can be avoided, or the number of current detectors can be further reduced.

It is a block diagram which shows the aspect by which an active filter control apparatus is employ | adopted in 1st Embodiment. It is a graph which shows R phase voltage, load current, direct current, and estimated R phase current. It is a graph which shows the R phase part of load current, compensation current, and power supply current. It is a block diagram which shows partially the aspect by which an active filter control apparatus is employ | adopted in 2nd this Embodiment. It is a block diagram which shows the technique compared with 2nd Embodiment. In 3rd Embodiment, it is a block diagram which shows the aspect in which an active filter control apparatus is employ | adopted partially. It is a graph which shows the process of a memory | storage device.

First embodiment.
FIG. 1 is a block diagram showing a mode in which an active filter control device is employed in the present embodiment.

  The three-phase AC power supply 1 supplies a load 2 with a three-phase load current Io (which collectively grasps the load currents ir, is, and it for each phase). The parallel active filter 6 is connected to the AC power supply 1 via a three-phase interconnection reactor 4. The parallel active filter 6 outputs a three-phase compensation current Ic.

  Here, the compensation current Ic is assumed to have a positive direction from the parallel active filter 6 to the AC power supply 1, and the sum of the power supply current Is flowing from the AC power supply 1 and the compensation current Ic is the load current Io. .

  Of course, even if the direction of the compensation current Ic is opposite to that in the description of the embodiment, it only changes the sign (positive or negative) of the polarity of the compensation current Ic.

  The load 2 is an air conditioner including a converter 21 composed of a diode bridge and a compressor (including a motor 24) that is controlled by an inverter 23 and compresses a refrigerant (not shown). The load 2 further includes a low-pass filter between the converter 21 and the inverter 23 in order to supply the DC voltage Vc to the inverter 23. The low-pass filter is a choke input type and includes a reactor 25 and a capacitor 22.

  Note that a DC current detector 26 is provided in the load 2, and a DC current idc flowing between the converter 21 and the inverter 23 is detected. Since the low-pass filter is a choke input type, the direct current idc can also be grasped as a current flowing through the reactor 25.

  The parallel active filter 6 includes an inverter 61 and a capacitor 62, for example. Inverter 61 inputs / outputs compensation current Ic to charge / discharge capacitor 62 to / from DC voltage Vdc. For example, the inverter 61 is a voltage source inverter, and three current paths are connected in parallel to the capacitor 62, and two switching elements are provided in each current path.

  Note that the low-pass filter 9 is desirably provided from the viewpoint of removing the ripple of the compensation current Ic. Here, the low-pass filter 9 is shown for only one phase, but in reality it is provided for three phases.

  The active filter control device includes a transformer 71, a phase calculator 72, dq converters 11 and 73, high-pass filters 74 and 75, a phase current calculator 76, a subtractor 77, a voltage controller 78, and an adder 79.

  The transformer 71 detects one phase of the three-phase voltage of the AC power supply 1 and supplies it to the phase calculation unit 72. The phase calculation unit 72 transmits the detected phase ωt to the dq converter 73 and the phase current calculation unit 76.

  The phase current calculation unit 76 calculates the three-phase currents ir ^, is ^, it ^ estimated as the load currents ir, is, it from the DC current idc detected by the DC current detector 26 based on the phase ωt. Perform the desired calculation.

  From the above, in the present embodiment, the phase calculation unit 72 and the phase current calculation unit 76 can be grasped as a current estimation measure by adding the DC current detector 26 or further.

  The dq converter 73 performs three-phase / two-phase conversion on the three-phase currents ir ^, is ^, it ^ to obtain the d-axis component and the q-axis component of the load current Io. The high-pass filters 74 and 75 remove low-frequency components, particularly DC components, of the d-axis component and the q-axis component. Further, the dq converter 11 performs three-phase / two-phase conversion on the compensation current Ic to obtain a d-axis current id and a q-axis current iq.

  Here, the d-axis and the q-axis are rotating coordinate systems that rotate in synchronization with the phase ωt detected by the phase calculation unit 72.

  The component of the load current Io that is synchronized with the phase of the AC power supply 1 appears as a DC component in the d-axis component and the q-axis component. That is, if there is no harmonic component in the load current Io, the d-axis component and the q-axis component are only DC components. Therefore, the high-pass filters 74 and 75 output only the harmonic component of the load current Io that appears as the d-axis component and the q-axis component.

  The subtractor 77 obtains a deviation between the DC voltage Vdc supported by the capacitor 62 and its command value Vdc *. The voltage controller 78 performs PI control (proportional integral control) on the deviation obtained from the subtractor 77 to obtain a correction value for the d-axis current. The correction value is added by the adder 79 with the output of the high-pass filter 74 (for d-axis current). As a result, the d-axis current command value id * is obtained from the adder 79.

  The q-axis current command value iq * is obtained from the high-pass filter 75 for q-axis current.

  It can be said that the d-axis current command value id * and the q-axis current command value iq * are obtained by grasping the harmonic component of the load current Io in consideration of the pulsation of the DC voltage Vdc in the rotating coordinate system.

  Therefore, if the d-axis current id and the q-axis current iq of the compensation current Ic match the d-axis current command value id * and the q-axis current command value iq * without a phase shift, the compensation current Ic becomes a harmonic of the load current Io. A component is borne, and no harmonic component is generated in the power supply current Is.

  Therefore, the d-axis current command value id * and the q-axis current command value iq * can be grasped as the command values for the d-axis current id and the q-axis current iq obtained by grasping the compensation current Ic in the rotating coordinate system.

  The active filter control device further includes subtractors 32d and 32q, current controllers 10d and 10q, and a drive signal generation circuit 8.

  The subtractor 32d subtracts the d-axis current id from the d-axis current command value id * to obtain a d-axis current deviation. The current controller 10d outputs a voltage command value Vid by performing PI control on the deviation.

  The subtractor 32q subtracts the q-axis current iq from the q-axis current command value iq * to obtain the q-axis current deviation. The current controller 10q outputs a voltage command value Viq by performing PI control on the deviation.

  The drive signal generation circuit 8 generates a drive signal G for driving the parallel active filter 6 based on the voltage command values Vid and Viq. For example, the drive signal generation circuit 8 generates a drive signal G by performing a logical operation on the result of comparing the voltage command values Vid and Viq with the carrier. Therefore, it can be said that the voltage command values Vid and Viq are control signals for controlling the parallel active filter 6 indirectly via the drive signal G.

  In such a configuration, feedback control is performed so that the d-axis current id and the q-axis current iq of the compensation current Ic coincide with the d-axis current command value id * and the q-axis current command value iq *. Therefore, the compensation current Ic bears the harmonic component of the load current Io, and no harmonic component is generated in the power supply current Is.

  In order for such feedback control to be performed appropriately, the three-phase currents ir ^, is ^, it ^ must be appropriately estimated as the load currents ir, is, it.

  As in the prior art, when at least two phases of the load currents ir, is, and it are detected, it must be clear to which phase the detected current corresponds. That is, when detecting the load currents themselves and supplying them to the dq converter 73, it is necessary to avoid erroneous connection of the current detectors for the two phases.

  Therefore, it is desirable to determine which phase each of the three-phase currents ir ^, is ^, and it ^ corresponds to, based on the phase ωt itself, not the connection location of the current detector. Details will be described below.

  In the following, it is assumed that the three phases indicate the R phase, the S phase, and the T phase, and the transformer 71 outputs the R phase voltage Vr of the AC power supply 1 to the phase calculation unit 72. Therefore, the phase ωt of the phase calculation unit 72 is the phase of the R-phase voltage Vr.

  In order for the transformer 71 to output the R-phase voltage Vr of the AC power supply 1 to the phase calculation unit 72, it is assumed that the transformer 71 is connected to the R-phase wiring. However, this is only necessary to avoid erroneous connection for one phase, and is simpler than avoiding erroneous connection of current detectors for two phases.

  FIG. 2 is a graph showing R-phase voltage Vr, load currents ir, is, it, DC current idc, and estimated R-phase current ir ^. On the horizontal axis, the phase of the R-phase voltage Vr is shown in “degrees” with time. However, the phase when the polarity of the R-phase voltage Vr changes from negative to positive is set to zero.

  FIG. 3 is a graph showing the load current ir, the R phase of the compensation current Ic, and the R phase of the power supply current Is.

  2 and 3, the converter 21 is illustrated as performing a full wave rectification.

  The converter 21 is configured by a diode bridge, and the direct current idc output from the converter 21 flows through the reactor 25. In such a configuration, if the power supply voltage is stable, the load currents ir, is, it are in a relationship shifted from each other by 120 degrees as shown in FIG. Further, each of them becomes zero in a period of 60 degrees apart from each other by a period of 120 degrees, and in a pair of 120 degrees periods sandwiching the period of 60 degrees, they exhibit waveforms having opposite polarities.

  When converter 21 performs full-wave rectification, DC current idc is obtained as a combination of waveforms on the same polarity side (positive side in this case) of load currents ir, is, it.

  The load current ir coincides with the DC current idc when the phase ωt of the R-phase voltage Vr is 30 to 150 degrees, the absolute value is the same as that of the DC current idc at 210 to 330 degrees, and the polarity is different. take.

  The load current is coincides with the direct current idc when the phase ωt of the R-phase voltage Vr is 150 to 270 degrees, and the absolute value is the same as that of the direct current idc at 330 to 360 degrees and 0 to 90 degrees. The phase takes the value 0.

  The load current it coincides with the DC current idc when the phase ωt of the R-phase voltage Vr is 270 to 360 degrees and 0 to 30 degrees, and at 90 to 210 degrees, the absolute value is the same as that of the DC current idc, and the polarity is different. The phase takes the value 0.

  Therefore, a period of 120 degrees of the voltage phase period is extracted from the DC current idc as a reference current from the DC current idc based on the phase ωt, and the current ir ^ can be obtained as follows.

  The phase ωt at the time when the polarity of the R-phase voltage changes from negative to positive is defined as 0 degree, and the phase ωt matches the direct current idc at (i) 30 to 150 degrees, and (ii) the direct current idc at 210 to 330 degrees. And (iii) a current that takes a value of 0 in other phases is a current ir ^ that is an estimated value of the R-phase load current ir.

  The current is ^ and it ^ may be obtained in the same manner as the current ir ^, or may be obtained by shifting the current ir ^ by 120 degrees and 240 degrees, respectively.

  The current ir ^ shown in FIG. 2 is almost equal to the load current ir shown in FIG. Thereby, the compensation current Ic is correctly controlled, and almost no harmonics are superimposed on the power source current Is.

  As described above, since the DC current idc is detected when the load currents ir, is, and it are estimated, the DC current detector 26 is sufficient for a single phase, and therefore erroneous connection is avoided.

Second embodiment.
FIG. 4 is a block diagram partially showing a mode in which the active filter control device is employed in the present embodiment. The components connected directly or indirectly to the dq converter 73, the phase calculation unit 72, the low-pass filter 9, and the converter 21 are the same as those in FIG.

  In the present embodiment, the DC current detector 26 of the first embodiment is removed, and a two-phase AC current detector 81a is employed. The alternating current detector 81a detects load currents iac1 and iac2 corresponding to any two phases of the load current Io. It does not ask which phase corresponds to these.

  FIG. 5 is a block diagram showing a technique compared with the present embodiment. Although the two-phase AC current detector 81a is employed as in the present embodiment, the load currents ir and is determined for which phase the dq converter 73 corresponds to must be detected.

  Thus, in this embodiment, the direct current idc is not detected. Instead, a direct current calculation unit 82 is provided, which obtains an estimated value idc ^ of the direct current idc from the load currents iac1 and iac2.

  Then, from the estimated value idc ^, the phase current calculator 76 obtains the three-phase currents ir ^, is ^, it ^ as in the first embodiment.

  Therefore, since the present embodiment does not ask in which phase the AC current detector 81a detects the load current with respect to the technology to be compared, as long as the load current in a different phase is detected, the problem of incorrect connection is not exist.

  In order to obtain such an advantage, it is necessary to appropriately obtain the estimated value idc ^ from the load currents iac1 and iac2. The method will be described below.

  The load current Io is a three-phase current, and the load current iac3 of the phase not detected by the two-phase AC current detector 81a is obtained by subtracting the sum of the load currents ia1 and iac2 from zero.

  As described with reference to FIG. 2 in the first embodiment, the load currents ia1, iac2, and ia3 are shifted from each other every 120 degrees. Further, each of them becomes zero in a period of 60 degrees apart from each other by a period of 120 degrees, and in a pair of 120 degrees periods sandwiching the period of 60 degrees, they exhibit waveforms having opposite polarities.

  Therefore, when converter 21 performs full-wave rectification, estimated value idc ^ is obtained as a composite of waveforms of load currents ia1, iac2, and ia3 on the same polarity side (in this case, the positive side).

  The DC current calculation unit 82 performs such processing, and can appropriately obtain an estimated value of the estimated value idc ^ of the DC current idc based on the load currents ia1 and iac2 whose phase is unknown. .

  That is, in the present embodiment, the phase calculation unit 72, the phase current calculation unit 76, and the direct current calculation unit 82 can be grasped as a current estimation device by adding the alternating current detector 81a.

  Thus, in this embodiment, the number of current detectors is not necessarily reduced as compared with the conventional case, but there is an advantage that the problem of incorrect connection can be avoided.

Third embodiment.
FIG. 6 is a block diagram partially showing a mode in which the active filter control device is employed in the present embodiment. The components connected directly or indirectly to the dq converter 73, the phase calculation unit 72, the low-pass filter 9, and the converter 21 are the same as those in FIG.

  In the present embodiment, a single-phase alternating current detector 81b is employed instead of the two-phase alternating current detector 81a of the second embodiment. The alternating current detector 81b detects the load current iac1 for one phase of the load current Io. This does not ask which phase it corresponds to.

  In this embodiment, a storage device 83 is added to the configuration shown in the second embodiment. The storage device 83 receives the load current iac1 and generates estimated values iac2 ^ and iac3 ^ for two phases of the load current Io not detected by the AC current detector 81b based on the phase ωt.

  The direct current calculation unit 82 obtains the estimated value idc ^ of the direct current idc from the load current iac1 and the estimated values iac2 ^ and iac3 ^ in the same manner as in the second embodiment.

  The phase current calculation unit 76 generates the three-phase currents ir ^, is ^, it ^ from the estimated value idc ^ in the same manner as in the first embodiment.

  Therefore, the alternating current detector 81b is sufficient for a single phase, and therefore erroneous connection is avoided. In order to obtain such advantages, it is necessary to appropriately obtain the estimated values iac2 ^ and iac3 ^ from the load current iac1. The method will be described below.

  As described with reference to FIG. 2 in the first embodiment, the load currents ia1, iac2, and ia3 are shifted from each other every 120 degrees. Therefore, the storage device 83 can store the waveform of the load current ia1 and shift it by 120 degrees or 240 degrees based on the phase ωt to obtain the estimated values iac2 ^ and iac3 ^ of the other two phases. . That is, the storage device 83 functions as a phase shifter.

  In the present embodiment, the phase calculation unit 72, the phase current calculation unit 76, the DC current calculation unit 82, and the storage device 83 can be grasped as a current estimation device by adding an AC current detector 81b.

  FIG. 7 is a graph showing processing of the storage device 83, and shows waveforms of the R-phase voltage Vr, the load current iac1, and the estimated values iac2 ^ and iac3 ^.

  FIG. 7 illustrates a case where the load current iac1 is a current for the R phase. However, once the estimated value idc ^ of the direct current idc is obtained as described above, the three-phase currents ir ^, is ^ and it ^ are obtained. Therefore, it does not matter which phase the load current iac1 corresponds to.

  In this way, when estimating the load current ir, is, it, only one of them is detected, so that the AC current detector 81b is sufficient for a single phase, and therefore erroneous connection is avoided.

21 Converter 22 Smoothing Capacitor 25 Reactor 26 DC Current Detector 72 Phase Calculation Unit 76 Phase Current Calculation Unit 81a, 81b AC Current Detector 82 DC Current Calculation Unit

Claims (7)

A diode bridge (21) for inputting a three-phase AC voltage, full-wave rectifying and outputting a DC current (idc);
A reactor (25) through which the direct current flows;
The power converter and a smoothing capacitor (22) connected in parallel with the series connection between the diode bridge and the reactor, the diode bridge the DC current (idc, idc ^) from which the diode bridge output A current estimation device for estimating an alternating current (ir, is, it) input to
A phase calculator (72) for detecting a voltage phase of the alternating voltage (Vr) of the first phase;
When the polarity of the AC voltage of the first phase changes from negative to positive, the voltage phase is set to 0 degree, and the voltage phase is
(i) said match the DC current at 30 to 150 degrees,
(ii) from said DC current in 210-330 degrees different polarity equal absolute value,
(iii) a phase current calculation unit (76) in which a current that takes a value of 0 in other phases is an estimated value (ir ^) of the alternating current (ir) of the first phase ;
A current estimation device comprising: a direct current detector (26) for detecting the direct current (idc) from the output side of the diode bridge . A diode bridge (21) for inputting a three-phase AC voltage, full-wave rectifying and outputting a DC current (idc);
A reactor (25) through which the direct current flows;
A smoothing capacitor (22) connected in parallel to the series connection of the reactor and the diode bridge;
A current estimation device that estimates an alternating current (ir, is, it) input to the diode bridge from the direct current (idc, idc ^) output from the diode bridge,
A phase calculator (72) for detecting a voltage phase of the alternating voltage (Vr) of the first phase;
When the polarity of the AC voltage of the first phase changes from negative to positive, the voltage phase is set to 0 degree, and the voltage phase is
(i) coincides with the direct current at 30 to 150 degrees,
(ii) At 210 to 330 degrees, the direct current has the same absolute value and different polarity,
(iii) a phase current calculation unit (76) in which a current that takes a value of 0 in other phases is an estimated value (ir ^) of the alternating current (ir) of the first phase;
The alternating current (iac3) of the other one phase is obtained from the alternating currents (iac1, iac2) of two phases, and the waveforms of the same polarity of the alternating currents of the three phases are synthesized, and the direct current ( DC current calculation unit (82) for estimating idc)
With
The phase current calculation unit (76) obtains an estimated value (ir ^) of the alternating current (ir) of the first phase from the direct current (idc ^) estimated by the direct current calculation unit. . AC current detector (81a) for detecting the AC currents (iac1, iac2) of the two phases
The current estimation device according to claim 2 , further comprising: A diode bridge (21) for inputting a three-phase AC voltage, full-wave rectifying and outputting a DC current (idc);
A reactor (25) through which the direct current flows;
A smoothing capacitor (22) connected in parallel to the series connection of the reactor and the diode bridge;
A current estimation device that estimates an alternating current (ir, is, it) input to the diode bridge from the direct current (idc, idc ^) output from the diode bridge,
A phase calculator (72) for detecting a voltage phase of the alternating voltage (Vr) of the first phase;
When the polarity of the AC voltage of the first phase changes from negative to positive, the voltage phase is set to 0 degree, and the voltage phase is
(i) coincides with the direct current at 30 to 150 degrees,
(ii) At 210 to 330 degrees, the direct current has the same absolute value and different polarity,
(iii) a phase current calculation unit (76) in which a current that takes a value of 0 in other phases is an estimated value (ir ^) of the alternating current (ir) of the first phase;
A phase shifter (83) for estimating the alternating currents (iac2, iac3) of the other two phases by shifting the phase of the alternating current (iac1) of one phase by 120 degrees or 240 degrees;
A direct current that estimates the direct current (idc) by synthesizing waveforms of the same polarity of the alternating current of the one phase and the estimated alternating currents (iac2 ^, iac3 ^) of the other two phases. Current calculation unit (82) and
With
The phase current calculation unit (76) obtains an estimated value (ir ^) of the alternating current (ir) of the first phase from the direct current (idc ^) estimated by the direct current calculation unit. . AC current detector (81b) for detecting the AC current (iac1) of the one phase
The current estimation device according to claim 4 , further comprising: A diode bridge (21) for inputting a three-phase AC voltage, full-wave rectifying and outputting a DC current (idc);
A reactor (25) through which the direct current flows;
A smoothing capacitor (22) connected in parallel to the series connection of the reactor and the diode bridge;
A current estimation device that estimates an alternating current (ir, is, it) input to the diode bridge from the direct current (idc, idc ^) output from the diode bridge,
A phase calculator (72) for detecting a voltage phase of the alternating voltage (Vr) of the first phase;
When the polarity of the AC voltage of the first phase changes from negative to positive, the voltage phase is set to 0 degree, and the voltage phase is
(i) coincides with the direct current at 30 to 150 degrees,
(ii) At 210 to 330 degrees, the direct current has the same absolute value and different polarity,
(iii) a phase current calculation unit (76) in which a current having a value of 0 in the other phases is an estimated value (ir ^) of the alternating current (ir) of the first phase;
With
The phase current calculation unit (76)
By shifting the phase of the estimated value (ir ^) of the alternating current (ir) of the first phase by 120 degrees or 240 degrees, the estimated value (is ^; it) of the alternating current (is; it) of the second phase ^) To obtain a current estimation device. The phase current calculation unit (76) shifts the phase of the estimated value (ir ^) of the alternating current (ir) of the first phase by 120 degrees or 240 degrees, so that the alternating current (is; it; estimate of) (is ^; it ^) obtaining a current estimation device of any one of claims 1 to 5.

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